1. Field of Invention
This invention relates to a low cost externally mounted retractable stern thruster to aid vessels in close quarters maneuvering.
2. Background of the Invention
The maneuvering of vessels in close quarters as in crowded harbors and while docking and undocking is difficult using only the vessel""s main propulsion system. Large commercial vessels address this problem through the use of tugboats. Smaller vessels may achieve sufficient control with on board systems that produce thrust in a direction perpendicular to the axis of the vessel. Such side thrust systems are well known. When mounted in the bow the system is known as a bow thruster and when mounted in the stern such systems are known as stern thrusters.
The hazards of close quarter vessel maneuvering have been addressed in the prior art. Numerous forms of bow and stern thrusters have been developed to provide side thrust. A basic internal bow thruster consists of a tube installed in the bow of a vessel below the waterline connecting the port and starboard sides of the hull. A drive unit with single or multiple propellers is installed within the tube. Screens to retain debris may also be installed. When activated the propellers provide side thrust to move the bow in the desired direction. A unit of this type is described in U.S. Pat. No. 6,009,822 to Aron. Internal bow thrusters normally are not installed in vessels less than ten meters due to space and cost considerations.
There are many problems associated with an internal bow thruster.
1. High installation cost
2. Potential reduction of structural integrity in the bow sections in normal use and in the event of a collision
3. Clogging of screens can reduce thrust
4. Marine growth can reduce thrust
5. High maintenance cost as the vessel must be dry-docked to service the unit
6. Increased drag resulting from the holes on either side of the bow below the waterline
7. Normally suitable only for vessels longer than ten meters
Thrusters have been developed which retract for servicing as in U.S. Pat. No. 6,056,610 to Fontanille. Such devices are practical only for very large vessels and suffer from problems 1, 2, 6 and 7 above.
An external bow thruster is noted in prior art U.S. Pat. No. 4,732,104 to Roestenberg. This device suffers from its exposed storage position on the leading edge of the bow of the boat. Rough sea conditions could damage or break the device loose. A collision with a floating or a fixed object would damage or break loose the device. Once the device is lowered it becomes even more vulnerable to damage. FIG. 1, item 10 is the topmost portion of a vessel""s bow and item 12 is the waterline at the bow. The great distance between items 10 and 12 illustrates the high risk associated with mounting an external bow thruster in the location between items 10 and 12.
A partial external bow thruster using water jets is described in U.S. Pat. No. 4,807,552 to Fowler. While the discharge streams in this device are above the waterline, the intake is below the waterline. This intake permanently below the waterline makes the unit vulnerable to leakage debris ingestion and marine growth performance degradation.
Stern thrusters are similar to bow thrusters in that a tunnel is created through the hull below the waterline at the stern of the vessel. Internal stern thrusters of this type suffer from the same problems enumerated above for internal bow thrusters.
A partial solution to an internal stern thruster is presented in U.S. Pat. No. 4,487,149 to Morris. This device utilizes a drive within a tunnel permanently mounted beneath the waterline of the vessel from the swim platform. FIG. 1, item 11 illustrates a typical swim platform. This system addresses the potential hazard of structural damage or leakage from an internal tube through the hull. All other problems associated with the internal bow thrusters apply to this device.
Accordingly several objects and advantages of my invention are:
(a) to provide a vessel maneuvering device whose attachments and power supply are all above the waterline.
(b) to provide a vessel maneuvering device that may be retracted when not in use so that said device is out of water precluding marine growth and corrosion performance degradation:
(c) to provide a vessel maneuvering device that is stored in a location when not in use where the device is not subject to damage from debris and high seas.
(d) to provide a vessel maneuvering device installation that is inexpensive compared to currently available devices
(e) to provide a vessel maneuvering device which does not detract from vessel performance when the device is not in use and the vessel is under way.
(f) to provide a vessel maneuvering device which may easily be removed for service or storage.
(g) to provide a vessel maneuvering device that may be equipped with a wide variety of hand or foot control systems.
(h) To provide a vessel maneuvering device that is economic, effective and practical for vessels below 10 meters as well as larger vessels.
(i) To provide a vessel maneuvering device that may be easily mounted and adapted to any vessel.
(j) To provide a vessel maneuvering device that may positioned for use and retracted for storage manually or by commonly available electrical, mechanical, hydraulic or pneumatic devices;
(k) To provide a vessel maneuvering device that may be operated at the device or anywhere on the vessel with commonly available controls.
(l) To provide a vessel maneuvering device that may be powered by electricity, hydraulics or pneumatics.
In accordance with the present invention a vessel maneuvering device which utilizes a thrust producing mechanism affixed to a deployment device which is attached to the stern of a vessel with no requirement for through hull openings below the waterline. Said deployment device allows said thrust mechanism to be moved between an operating position in the water and a safe storage position out of the water.